Conventionally, the work of grooving a tire for trial manufacturing and limited scale production, namely carving the tread pattern grooves in a plain cured tire without any tread pattern is generally performed by means of a hand cutter, requiring skill and a lot of time.
Taking the above-mentioned problem into consideration, the present applicant has proposed a tire grooving apparatus, as shown in FIG. 32, having, as main constructive features, a cutting device attached to a vertically movable carriage, which is moved in parallel and perpendicular directions against the tire support shaft; a pivotable arm support shaft which is extended from the carriage; a pivotable arm attached to the support shaft; a cutter holder which is pivotably attached to the pivotable arm perpendicular to the axis thereof; a cutter which is held by the end portion of the cutter holder; and the cutting position of the cutter arranged to be on the extended axis of the support shaft (Japanese Unexamined Patent Publication No. 54240/1988 and 177232/1986).
In the present specification, the cutting position of the cutter refers to a peculiar point of the cutter which is a certain distance (M) (including zero) from the bottom end of the cutter holder (refer to FIG. 1).
Carving of tread pattern grooves for a plain tire by the tire grooving apparatus is carried out by setting the cutting position of the cutter to the tangential line (Processing Standard Point for Tread) of a plain tire. Thus, since the cutting position of the cutter is maintained on the extended axis of the pivotable arm support shaft, namely on the tangential line of the plain tire, calculation of quantity of movement of the movable carriage and the pivotable arm becomes simple, the programming of computer programs becomes easy and accurate grooving becomes possible.
However, when lateral runout in the tire-width direction caused by strain of the tire itself or deviation of the tire support occurs, even if grooving is carried out by the cutter of which movement is controlled by a computer program so as to carve the prescribed tread pattern while the tire is rotated, the position of grooves from the tread center of tires of the same size and specification differs for each tire and positions of grooves which ought to be on right and left sides of the tread center C (the tire equator) are different for each groove when a plurality of grooves are carved in a tire, so that quality problems arise such as variations in tire quality and decreased strength.
To solve these problems, the present applicant has provided a tire grooving apparatus and method, wherein the lateral runout of the tire is detected and the cutting position of the cutter is corrected in accordance with detected value.
However, even if the same kind of tires are attached to the tire supporting shaft of the tire grooving apparatus in the same way, the tread center position does not always coincide with the theoretical tread center position set by the standard program for each tire and slight deviation sometimes occurs because of the difference in dimensions on the right and left sides of the tire which arise during curing, deformation caused by inner pressure, the improper engagement with a rim and like.
Accordingly, as shown in FIG. 19, the quantity y of lateral runout on the side of the tire is not always equal to the quantity of actual deviation of tread center TC to the tread center PC set by the standard program. Therefore, even if the lateral runout on the side of the tire is detected and the position of the cutter is corrected with the detected value (the cutter is moved to follow the lateral runout) and thereby the grooving is performed, the position to be cut cannot be set to a prescribed distance from the tread center of the tire. Finally, the position of tread grooves from the tread center TC does not coincide with each tire of the same kind.
Taking the above-mentioned problems of the conventional art into consideration, it is an object of the present invention to provide a tire grooving apparatus and method wherein position of the cutter is corrected such that for any position of tread grooves from the tread center, coincide among tires of the same kind and are formed at tread groove positions of a tire to prescribed positions on the right and left sides of the tread center.